1. Field of the Invention
The present invention is directed to an optical element having a single surface which both diffuses light and has optical power.
2. Description of Related Art
Diode lasers, LEDs and other light sources produce beams having a nonuniform power distribution. This non-uniformity is often detrimental to performance of a system. It is difficult to achieve uniform power distribution using a conventional lens system. Elements which could be used to re-map the power distribution to one having uniform illumination are desirable for many applications.
It is advantageous to use a diffractive diffuser as shown in FIG. 1, to provide the desired uniform illumination. The diffractive diffuser in FIG. 1 is discussed in detail in U.S. application Ser. No. 08/770,524 entitled "Beam Homogenizer" filed Dec. 20, 1996, which is hereby incorporated by reference in its entirety. In FIG. 1, an incident optical beam 14, preferably a collimated beam, illuminates a diffractive diffusing element 10. The diffractive diffusing element is preferably a computer-generated hologram having irregularly patterned, free-form fringes of diffractive gratings 12. The diffractive fringes 12 of the preferred embodiment are made up of plateaus 16, shown as white areas and presenting a phase shift of zero at the design wavelength to the input beam 14, and vias or valleys 18, shown as black areas and presenting a phase shift of .pi. at the design wavelength to the input beam. Such a homogenizer eliminates undesired intensity variations encountered when using a homogenizer having regularly shaped, regularly patterned facets.
The diffractive diffuser 10 transmits transmittal beams 11a, 11b, 11c having a preselected angular spread which provides a beam having uniform illumination at a target 20 in an output plane 22. The output plane 22 represents an area in space rather than any particular element. It would be possible to place another optical element or any device which would make use of the output beam downstream. Any area of sufficient size, i.e., to insure that the full range of line widths present in the pattern, at any position on the diffuser 10 will provide this angular spread to the input beam 14. Each area of sufficient size is nominally uncorrelated to another area of similar size. The choice of angular spread depends upon the application for which the homogenizer is used and the desired output beam.
Often, it is desirable to deflect or focus an image, as well as to diffuse it. However, due to space considerations for some applications, it is not convenient to insert an additional optical element for providing diffuse illumination. Further, there is an additional expense associated with making an additional element.